Injection overmolding generally comprises coating a substrate placed inside a mold with a liquid, powder and/or slurry plastic (hereinafter referred to as “molten plastic”) at relatively high temperatures. The molten plastic is usually injected into the mold at high pressures or at low pressures, depending on the application and the type of substrate. Low pressure injection overmolding is typically done with injection pressures ranging from 10-40 MPa (100-400 bar), while high pressure injection overmolding is typically done with injection pressures ranging from 80-200 MPa (800-2000 bar). Generally, for structurally reinforced, molded plastic parts, the substrate may comprise a tube, a profile, or some other shaped, rigid element adapted to resist the high temperatures and pressures associated with injection overmolding.
There are advantages to using high pressure injection overmolding in the fabrication of structurally reinforced, molded plastic parts. For example, moduli of elasticity, impact resistance, puncture resistance, and other mechanical characteristics, are substantially improved in reinforced parts produced by high pressure injection overmolding compared with parts produced by low pressure injection overmolding. Additionally, thickness of a plastic coating may be substantially reduced when using high-pressure injection overmolding, providing for a relative saving in manufacturing costs while also maintaining anticorrosion characteristics.
Generally, substrate design requirements include a use of profiles which are rigid, lightweight, and fabricated from relatively inexpensive materials. Furthermore, the profiles are generally required to be of sufficient strength to not deform and/or suffer other mechanical degradations, as a result of a force with which the molten plastic strikes the profiles when injected into the mold at high pressure. Usually, in order to prevent deformations and/or other mechanical degradations, profiles with relatively thick walls, for example. greater than 3 mm are typically used. The use of profiles with relatively thick walls is generally a problem as the profiles may have a tendency to be relatively heavy in weight.
US Patent Application Publication No. 2007/0071929 A1, “Molded Article with Metal Reinforcing and Method for its Manufacture”, incorporated herein by reference, describes “a composite article comprises a channel-shaped metal reinforcing element and molded plastic shell including a portion formed as a wall mechanically closing the open side of the channel shape. The reinforcing element may include a plurality of open channels each of them being closed by a portion of the plastic coating. Constructive elements comprising at least two such composite articles may be manufactured, for example a flat panel made of parallel elongated beams. A method for manufacturing the composite article in an assembly mold includes inserting a mold core in the metal reinforcing element via the open side of the channel transversely to the channel axis, assembling all parts of the mold, molding of the plastic coating, disassembling the mold; and removing the mold core from the composite article in direction parallel to the channel axis.”
European Patent Application EP 1238773 A1, “System for Overmolding Tubes in Plastic Parts”, incorporated herein by reference, describes a “system for overmoulding tubes in plastic parts, in which a tube, generally metallic and thin, is housed in the interior or a mould for its overmoulding, in that the tube is arranged on the supports in the said interior of the mould ins in that the filling is carried out with the plastic material in order to obtain a plastic structure in which the tube is fastened to the said structure, with the interior of the tube being completely free of any plastic material at the end of the overmoulding due to its being closed during the process, which is characterized in that while the overmoulding of the tube is taking place, means are provided in the interior of the tube to keep the shape of the tube unalterable by withstanding the external pressure exerted by the plastic material, with the application of these means being maintained until the part has been cooled and then proceeding to remove them once the part has been finished.”
Japanese Patent Publication No. 63141713 A, “Suction Pipe Made of Synthetic Resin for Engine and its Manufacture”, incorporated herein by reference, describes a method “to enable the suction path having two dimensional or mote complicated shape which is not capable of molding by injection molding to be achieved, while enabling ensuring the shape and the surface accuracy of a flange part which is not capable of molding by flow molding to be achieved by means of using the core in which the blow molding becoming the suction path of inner layer after molding is filled with sand, etc.” A drawback with the method described may be the possible combining of sand with the melted plastic, which may affect the surface finish of the reinforced part. To avoid this, tight production controls may be required, possibly resulting in increased production costs and production time.